Net Loss per Share - Additional Information (Details)	12 Months Ended
	Jan. 31, 2020 $ / shares shares	Jan. 31, 2020 shares $ / shares	Jan. 31, 2020 vote $ / shares shares	Jul. 31, 2018 $ / shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Initial conversion price (in dollars per share)	$ 211.20	$ 211.20	$ 211.20	$ 68.15
Class A Common Stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Number of votes		1	1
Class B Common Stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Number of votes		10	10
2024 Notes | Convertible Debt
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Shares issuable upon conversion (in shares) | shares	4,400,000	4,400,000	4,400,000
Initial conversion price (in dollars per share)	$ 68.15	$ 68.15	$ 68.15
Average market price	$ 139.22
2026 Notes | Convertible Debt
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Shares issuable upon conversion (in shares) | shares	5,400,000	5,400,000	5,400,000
Initial conversion price (in dollars per share)	$ 211.20	$ 211.20	$ 211.20